I think you've hit it on the head. They have changed to a system which weights repayment data, indeed the most weight is given to recent repayment data (last 3 months). In your case you have one account closed some time ago, i.e. they have no recent positive data for you. From the number of complaints here it sounds like they were somewhat premature to start using a comprehensive credit score with enough data in the system to support its use.Just another data point...
My last Credit Card application was in June 2017 (yes, slack, I know...).
My last 11 month’s credit scores (according to CreditSavvy) were all 724.
Then this month, following the introduction of the new CCR system, my score dropped to 565.
As far as I can see, the only change to the data they have is the addition of payment information on one credit card account (which has been closed for about 18 months), which shows a credit limit of $zero and a Repayments On Time history of 100%.
I have a ‘Real Life’ 100% pay on time record, and significant assets & income.
I know that the rating agencies are trying to produce scores on the basis of information which is known to be incomplete. But when any rational assessment of my ‘Real, full fact’ financial history & situation would probably result in a credit score of 950+ Vs the current 565, the system looks to be a bit broken & unreliable.
/end of grizzle...
On the plus side I think its irrelevant to compare you old score vs new if the basis has totally changed and it sounds like this current issue is across many people not just yourself. I haven't seen many (I think only one) report of a better score since this weekends changes.
Tis should all change as more data is contributed to the system of course. Also Experian is the lesser preferred of the two main agencies with credit providers and I don't think they have done themselves and favours in rushing this score to the market before its really ready.